Many polyfluorocarboxylic acids, in particular perfluoroalkanecarboxylic acids and 2-(perfluoroalkyl)ethanecarboxylic acids, are already known. These acids and their derivatives have found many uses, for example as wetting agents or surfactants or as intermediates for the preparation of agents for the treatment of textiles, leather or paper.
Chlorofluorocarboxylic acids are also known. But, in most cases, the chlorine and the fluorine are bound to the same carbon atoms as, for example, in the acids Cl(CF.sub.2 CFCl).sub.n --COOH described by R. N. Haszeldine, J. Chem. Soc., 4291-4302 (1955), or a --CCl.sub.2 -- bridge interrupts the perfluorinated chain, as, for example, in the acid CF.sub.3 --CCl.sub.2 --CF.sub.2 --COOH described by B. Boutevin et al., Eur. Polym. J., 12(5), 283-8 (1976).
However, only a few compounds are at present known in which the acidic functional group is linked to a perfluoro radical via a --CCl.sub.2 -- bridge. These compounds are, more specifically, 2,2-dichloro-3,3,3,trifluoropropionic acid, its chloride and its alkyl esters, J. D. Park et al, J. Org. Chem., 21, 220-2 (1956), prepared from 2,2-dichloro-3,3,3-trifluoropropenyl ethyl ether. The fluoride of this acid, which is usable for the preparation of surfactants, impregnating agents or herbicides, has also been described in German Patent No. 1,900,758 where it is prepared by the action of sodium fluoride or potassium fluoride on hexachloroacetone.
The preceding references are hereby incorporated by reference.